Tailored index single mode optical amplifiers and devices and systems including same

ABSTRACT

A semiconductor laser device includes a tailored index single mode power amplifier. A high-power laser system can be produced by connecting several of the tailored index single mode power amplifiers in parallel. In an exemplary case, a phase shifting device can be optically coupled to each of the tailored index single mode power amplifiers; the phase shifting devices can be controlled to ensure that the laser beams output by the tailored index single mode power amplifiers are both phase aligned and wavefront matched.

RELATED APPLICATIONS

[0001] This is a Continuation-in-Part application of Ser. No.09/547,302, which was filed on Jul. 28, 2000. The present applicationalso claims priority from Provisional Patent Application Nos. 60/232,880(Sep. 15, 2000) and 60/233,437 (Sep. 18, 2000). Each of theseapplications is incorporated herein by reference in its entirety for allpurposes.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to optical phased arrays.More specifically, the present invention relates to optical phasedarrays having a tailored real index, guided amplifier structure.Advantageously, methods of fabricating an optical phased array having atailored real index, guided amplifier structure, and systems employingthe optical phased array monolithic device (e.g., a coherent chip) alsodisclosed.

[0003] Semiconductor lasers are the fundamental building blocks incompact optic and optoelectronics devices. Formed from Group III-Vsemiconductors, semiconductor lasers emit laser light in response toelectrical stimulation, i.e., as electrons relax back to lower energystates, they emit photons. Stated another way, one of the mostsignificant developments in semiconductor technology in recent years hasbeen the increased use of III-V materials such as gallium arsenide andindium phosphide, and their ternary and quaternary alloys such asindium-gallium-arsenide-phosphide, as the active materials ofsemiconductor devices. The band gap characteristics of such materialstypically make them candidates for optoelectronic and photonicapplications such as lasers, light emitting diodes and photodetectors.For integrated circuit use, their high electron mobility often makesthem preferable to the more commonly used semiconductor, silicon.

[0004] Fabrication of such devices generally requires epitaxial growthof one or more layers on a single-crystal substrate. Epitaxial growthrefers to a method of depositing a material on a substrate such that thecrystal structure of the deposited material effectively constitutes anextension of the crystal structure of the substrate.

[0005] The three broad classes of methods for deposition by epitaxialgrowth are liquid phase epitaxy, vapor phase epitaxy and molecular beamepitaxy (MBE), which respectively involve deposition from a liquidsource, a vapor source and a molecular beam. One particularly promisingform of vapor phase epitaxy is a method for deposition from a gasincluding a metalorganic compound, i.e., metalorganic chemical vapordeposition (MOCVD). MOCVD processes make use of a reactor in which aheated substrate is exposed to a gaseous metalorganic compoundcontaining one element of the epitaxial layer to be grown and a gaseoussecond compound containing another element of the desired epitaxialmaterial. For example, to grow the III-V material gallium arsenide, onemay use the metalorganic gas triethylgallium [(C₂H₅)₃Ga] as the galliumsource and arsine (AsH₃) as the source of the group V component,arsenic. The gas mixture is typically injected axially at the top of avertically extending reactor in which the substrate is mounted on asusceptor that is heated by a radio-frequency coil. The gases areexhausted from a tube at the end of the reactor opposite the input end.Recently, the use of selective area growth (SAG) epitaxy, sometimesreferred to as selective area epitaxy (SAE) in the manufacture ofoptoelectronic components has increased chip functionality by increasingthe integration of more components on a single device (e.g. beamexpanded laser, electromodulated lasers.

[0006] High brightness semiconductor lasers of the type discussed aboveare generally single mode waveguide structures that are limited to a fewhundred milliwatts. It will be appreciated that higher power laserdevices and systems are desirable. However, prior efforts to increasethe power of conventional semiconductor laser devices via a larger gainregion have met with limited success. Many tapered semiconductor laserare designed as free expansion devices in a gain guided region with nocontrol over the position of the beam waist. In the resultant device, asthe carrier concentration increases with drive current, the anti-guidingeffects in the waveguide force the beam waist to shift. Many of thedevices exhibit an effective shift in the direction of propagation ofthe beam, which makes it very difficult to match the output beam to adownstream micro-optic element. This anti-guiding effect can cause thefar-field mode to increase in divergence as well as steer the beam as afunction of the drive current.

[0007] In an effort to alleviate or at least mitigate the latterproblem, a phased array of flared (tapered) amplifiers fed by phaseadjusters and a power splitter producing a single high power beam whenthe flared amplifier sections are aligned and closely spaced wasproposed in a paper by M. S. Zediker et al. entitled “10-AmplifierCoherent Array Based on Active Integrated Optics.” In the proposeddevice, which is illustrated in FIG. 1, a monolithic structure 20includes an injection port 22, for receiving a beam generated by, forexample, a master oscillator (not shown), an active distribution network24 comprising turning mirrors 24 a and Y-branch sections 24 b, phasemodulators 26, tapered optical power amplifiers 28, and lateral beamspreading guides 30. It will be appreciated that the output of thedevice 20 consists of, for example, 10 beams, which can be collimatedand combined by downstream optical elements (also not shown). It shouldbe mentioned at this point that it was envisioned that all of the phasemodulators will be employed to ensure that all of the output beams willbe phase aligned irrespective of the optical path length associated witha respective one of the output beams. It will be appreciated that, whilethe paper explains some of the difficulties inherent in fabricating aphased array of flared amplifiers, particularly with respect tomaintaining single mode operation in all of the amplifier regions of thedevice, the paper tacitly admits that a practical device was beyond thecapability of existing fabrication techniques.

[0008] Other devices employing a tapered or flared amplifier, such as amaster oscillator power amplifier (MOPA), which uses a distributed Bragggrating (DBG) to define a master oscillator while employing a taperedsection of the waveguide as a power amplifier, have been proposed. Forexample, a device similar to that disclosed by the Zediker et al. paper(discussed above) is disclosed in U.S. Pat. No. 5,440,576 to Welch etal. As illustrated in FIG. 2, a monolithic device 10 includes a firstportion containing a DBR master oscillator 12 having an active regionfor lightwave generation, which is bounded by a pair of distributedBragg reflectors 14 and 16, receiving power via a contact 18 connectedto wire 20, a second portion including a waveguide 22 and a powersplitter network 24, a third portion including a plurality of phaseadjusters 68, 70, 72 and 74, and a fourth portion including flaredamplifiers 78, 80, 82 and 84. The '576 patent discloses that the desired“phasing” is achieved by interfering outputs of less than all of theelements in the array; each interference pattern is adjusted for maximumcontrast using the phase modulator associated with a flared amplifierfrom which an interfering beam portion emanates.

[0009] However, in disclosing this device, the '576 patent does notspecify or even address the tailored index guide requirement needed tomake the taper amplifiers work effectively, particularly at high powerlevels. Consequently, this design has the substantial shortcomingsinherent in state-of-the-art devices at the time, i.e., circa 1994.Moreover, it will be appreciated that if the tapered amplifiers employedin the Welch et al. device have a constant index step, then the outputpower will be limited by the inability to maintain the single modecharacteristics over the entire length of the taper. This would forcethe designer to either underconfine the mode in the narrow sections, orloosely confine the mode in the wider sections. If the mode isunderconfined, then the propagation losses will be substantial and thepower that reaches the power amplifier section will be insufficient togenerate the desired output power. If the mode is loosely confined, thenthe anti-guide effects will be important, and the beam waist andfar-field profile will be affected in the manner described above.

[0010] It should be mentioned here that all of the papers and patentsmentioned herein are incorporated by reference. In particular, each ofthe patents mentioned by number is incorporated herein by reference inits entirety.

[0011] Accordingly, there is a need for an improved semiconductoramplifier structure. Stated another way, what is needed is a method forfabricating a tapered power amplifier having a corresponding tailoredindex profile suitable for ensuring single mode operation, and a stablebeam waist and astigmatism over a broad range of drive currents. What isalso needed is an optical phased array device having such a tailoredindex guided tapered amplifier structure. It would be beneficial if thedevice including an optical phased array having a tailored index guidedtapered amplifier structure could be employed in an optical amplifierallowing signals from many tapered amplifiers to be coherently combinedon a single optical fiber. It would be beneficial if the deviceincluding an optical phased array having a tailored index guided taperedamplifier structure permit coherent combination and steering of afar-field beam of advantageous profile through either a clear medium ora phase corrupting medium. Moreover, what is needed is an opticalamplifier that minimizes the number of lossy elements employed in thenetwork while minimizing the loss of signal-to-noise ratio through thedevice. Furthermore, it would be beneficial if the optical amplifiercould be injection locked to a common optical signal with a plurality ofother similar optical amplifiers, and arbitrarily phased to the opticalsignal such that the output beams from all of optical amplifiersadvantageously can be coherently combined to form a far-field beam ofadvantageous shape even in the presence of an inhomogeneous index mediumsuch as long paths through the atmosphere.

SUMMARY OF THE INVENTION

[0012] Based on the above and foregoing, it can be appreciated thatthere presently exists a need in the art for an optical phased arrayincorporating an index guided tapered amplifier structure whichovercomes the above-described deficiencies. The present invention wasmotivated by a desire to overcome the drawbacks and shortcomings of thepresently available technology, and thereby fulfill this need in theart.

[0013] According to one aspect, the present invention provides asemiconductor device having at least one tailored index single modeoptical power amplifier. If desired, the tailored index is produced bytailoring a current profile applied to the amplifier along at least theoptical axis of the semiconductor laser device. Alternatively, thetailored index associated with the power amplifier is produced byvarying the thermal impedance characteristic at the junction between thepower amplifier and a supporting heatsink. In another exemplaryembodiment, the tailored index associated with the power amplifier isprovided by implantation of impurities in the amplifier structure.Beneficially, the tailored index associated with the power amplifier canalso be provided by implanting impurities in regions of thesemiconductor laser device adjacent to the amplifier structure. Thetailored index associated with the power amplifier can be produced byvarying the height of the buried rib along the optical axis as the widthvaries from a first to a second predetermined value. Finally, thetailored index associated with the power amplifier can be produced by anumber of discrete, effective index steps that collectively form thedesired tailored index profile.

[0014] According to another aspect, a semiconductor laser deviceincludes an optical phased array having N power amplifiers connected inparallel, wherein each of the N power amplifiers is a tailored indexguided single mode power amplifier; and N is an integer greater than orequal to 2.

[0015] According to yet another aspect, the present invention providesan integrated semiconductor laser device, which generates N phasealigned, wavefront matched laser beams from N amplified laser signals.Preferably, the integrated semiconductor laser device includes N (N−1)phase modulators receiving an input beam from a master oscillator andgenerating N (N−1) phase shifted laser signals (and a reference signal);N tailored index single mode power amplifiers receiving the N (N−1)phase shifted laser signals (and the reference signal) and generatingthe N amplified laser beams. Another aspect of the present inventionprovides for the packaging of the integrated semiconductor device with aphase sensor generating N (N−1) sensor signals indicative of the phaseof the individual N (N−1) amplified laser beams; and a controller forcontrolling the phase of each of the N (N−1) amplified laser beamsresponsive to the N (N−1) sensor signals, respectively, to therebygenerate the N phase aligned, wavefront matched laser beams. In anexemplary embodiment, N is any positive integer.

[0016] According to a further aspect, the present invention provides asemiconductor laser system including:

[0017] N tailored index single mode power amplifiers, N being anypositive integer;

[0018] N (N−1) phase modulators optically coupled to the input ports ofthe N tailored index single mode power amplifiers;

[0019] an optical device which launches the output of the N tailoredindex single mode power amplifiers into an optical fiber to therebygenerate N coherent beams;

[0020] a phase sensor for generating respective electrical signalsindicative of phase and wavefront characteristic each of the N coherentbeams; and

[0021] a controller electrically coupled to the N (N−1) phase modulatorsfor permitting the N phase modulators to match the phase and wavefrontof the N coherent beams to one another.

[0022] Alternatively, the phase control of the chip can be accomplishedby monitoring the power captured in the central lobe of the far-field ofthe phased array. This far-field is generated either at the focal pointof a lens, or by placing a detector at least one Raleigh range away fromthe chip, where the Raleigh range is determined with respect to thephase aligned chip and not the individual emitters. The feedback signalneeded for phase control of the chip(s) can be derived by a digital (oranalog) phase check on each emitter, which translates to a change inintensity in the main lobe of the far-field as well as the side lobes inthe far-field. As optimum phase alignment is achieved, the on-axis mainlobe is maximized and the off-axis side-lobes are minimized. It shouldbe mentioned that the off-axis side-lobes are best suited to achievingnear ideal phase alignment because of the substantially enhancedsignal-to-noise ratio (SNR) of the phase dither compared to the dithersignal associated with the on-axis lobe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] These and various other features and aspects of the presentinvention will be readily understood with reference to the followingdetailed description taken in conjunction with the accompanyingdrawings, in which like or similar numbers are used throughout, and inwhich:

[0024]FIG. 1 illustrates a proposed optical phased array amplifier;

[0025]FIG. 2 illustrates a typical master oscillator power amplifier(MOPA) employing an optical phased array similar to that depicted inFIG. 1

[0026]FIGS. 3A, 3B, 3C, and 3D illustrate various layer arrangements,which advantageously can be employed in the construction of monolithicstructures such as laser diodes;

[0027]FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, and 4H illustrate variousaspects regarding the construction and of single and multiple taperedamplifier structures according to the present invention;

[0028]FIGS. 5A and 5B illustrate first and second preferredconfigurations of an optical phased array having an index guided taperedamplifier structure according to the present invention;

[0029]FIG. 6 illustrates an alternative configuration of an opticalphased array having an index guided tapered amplifier structureaccording to the present invention;

[0030]FIGS. 7A and 7B illustrate alternative formations of a turningmirror applicable to both deep trench and surface waveguides employablein the optical phased arrays depicted in FIGS. 5A, 5B, and 6;

[0031]FIG. 8 illustrates an integrated package containing the opticalphased arrays depicted in FIGS. 5A, 5B and 6 on a micro-channel coolerstructure;

[0032]FIGS. 9 and 10 illustrate alternative structures for wavefrontsampling, which can be employed for, in an exemplary case, theintegrated package illustrated in FIG. 8;

[0033]FIGS. 11A and 11B are useful in understanding the operatingcharacteristic of the tailored index single mode guided taperedamplifier according to the present invention;

[0034]FIGS. 11C and 11D are useful in understanding the operatingcharacteristic of a conventional optical phased array and an opticalphased array having a tailored index single mode guided taperedamplifier array according to the present invention;

[0035]FIG. 12 illustrates one exemplary technique for launching a veryhigh power laser beam generated by an optical phased array having atailored index single mode guided tapered amplifier structure into asingle mode optical fiber; and

[0036]FIGS. 13 and 14 illustrate exemplary embodiments of twodimensional optical phased arrays and supporting structure according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Illustrative embodiments and exemplary applications will now bedescribed with reference to the accompanying drawings to disclose theadvantageous teachings of the present invention.

[0038] While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those havingordinary skill in the art and access to the teachings provided hereinwill recognize additional modifications, applications, and embodimentswithin the scope thereof and additional fields in which the presentinvention would be of significant utility.

[0039] It will be appreciated that the monolithic devices such as thoseillustrated in FIGS. 1 and 2 can have the cross section illustrated ineither FIG. 3A or FIG. 3B. Thus, an optical waveguide advantageously caninclude a substrate 110, which is suitable for selective area epitaxy(SAE) laser device growth, above which is disposed a lower wide-gaptransverse waveguide outer confining layer 120, followed by a compositeactive region 130, which typically consists of a quantum well or wellsand appropriate inner barrier layers. The two layers 140 and 160disposed above the quantum well layer serve as the upper wide-gaptransverse waveguide outer confining layer. It will be appreciated thatthe layers 140 and 160 may have either similar or dissimilar materialcompositions, depending on a number of design factors well understood byone of ordinary skill in this particular art. A contact layer 170typically is a heavily-doped narrow gap layer suitable for formation ofhigh quality ohmic contacts. A rib element 150 is disposed between thelayers 140 and 160.

[0040] It will be noted that the selectively grown or etched ribstructure 150 is designed to have a narrower bandgap than the confininglayers 120, 140 and 160, thus, a higher refractive index. Tailoringdimensions of the rib layer 150, such as the thickness, width, andseparation and composition can be used to raise the effective refractiveindex in the central, or core, region, resulting in a latent slabdielectric waveguide.

[0041] It will also be noted that the configuration illustrated in FIG.3B is similar to that illustrated in FIG. 3A but for the thickness ofthe confining layer 140. In FIG. 3B, the confining layer 140 has a zerothickness, i.e., it is omitted; thus, the rib structure 150 is disposedimmediately adjacent to the quantum well layer 130. It should be notedthat the Zediker et al. paper mentioned above discussed the need forcontrolling the spacing between the rib element 150 and the active(quantum well) layer 130.

[0042] Other configurations are possible. For example, as illustrated inFIG. 3C, the monolithic device can be constructed as follows. Themonolithic structure includes a N-type GaAs substrate layer 110, aN-type cladding layer 120, an N-type waveguide layer 140, an active(quantum well) layer 130, a P-type waveguide layer 145, a rib layer 150,a P-type cladding layer 160, and a P-type cap layer 170, arranged in thestated order. In contrast, FIG. 3D illustrates a heterostructure device,which is fabricated with a N-type GaAs substrate layer 110, a N-typecladding layer 120, a rib structure including an N-type waveguide layer140, an active (quantum well) layer 130, a P-type waveguide layer 145, arib layer 150, which rib structure is covered with both a P-typecladding layer 160 and a P-type cap layer 170.

[0043] As previously mentioned, the use of selective area growth (SAG)epitaxy or selective area epitaxy (SAE) in the manufacture ofoptoelectronic components has increased chip functionality by increasingthe integration of more components on a single device. The onedistinction that must be made is that the SAG Epitaxy employed infabricated preferred embodiments according to the present inventionrefers to the growth through a mask that does not necessarily refer tothe desired thickness variance in the grown areas that are required inthese design. This growth through a mask can be performed with virtuallyany of the growth methods listed above. The SAE process takes advantageof the limited diffusion length of the gas borne species in the MOCVDtechnique to produce an enhanced growth rate in the unmasked crystalsurface. This enhanced growth rate is achieved through the carefuldesign of the mask to force the gas borne species to diffuse to theexposed crystal surface at a higher rate than in the areas that arewidely exposed. As a consequence, narrow unmasked regions advantageouslycan be forced to grow at a faster rate than wider unmasked regions andproduce the desired tailored rib profile, which profile is necessary toproduce the tailored index profile in exemplary embodiments of thepresent invention.

[0044] It should be mentioned at this point that all of the structuresillustrated in FIGS. 3A-3D advantageously can be formed by one or moreepitaxial growth processes. For example, the structure illustrated inFIG. 3C can be fabricated using MOCVD to grow entire structure;alternatively, MBE can be used to grow up to the p-waveguide layer 145followed by MOCVD Selective Area Epitaxial (SAE) growth of rib 150 andovergrowth of p-clad and p-cap layers 160 and 170. Moreover, withrespect to FIG. 3D, either MOCVD or MBE processes can be employed togrow all of the layers followed by patterned etching to create thedesired trench structure followed by SAE-MOCVD growth to create theproper rib feature followed by MOCVD overgrowth over entire structure tobury it. Alternatively, the MBE process can be employed during layergrowth through a mask followed by SAE-MOCVD growth to create the properrib feature, followed by MOCVD overgrowth over entire structure to buryit. The processes employed in generating structures such as taperedamplifier devices employing the layer arrangements illustrated in FIGS.3A and 3b will be discussed in greater detail immediately below.

[0045] It will be appreciated that tapered waveguide structures havebeen successful in extending power output of these devices to a fewwatts. See U.S. Pat. No. 5,440,576 to Welch et al., which was discussedin detail above. In contrast, U.S. Pat. No. 5,896,219 to Wandernothdiscloses another optical semiconductor amplifier with an integraloptical waveguide 180, i.e., a single tapered amplifier whose lateralextension increases over its length. Light guided in an optical inlet181 undergoes amplification on the way to the optical outlet 182 bymeans of stimulated emission of light in a distributed semiconductorjunction, which has been inserted into the optical waveguide 180 and ispumped with electrical current, wherein, because of the lateralextension of the optical waveguide 180, a small change results in theintensity of the amplified light in comparison to the light present atthe optical inlet 181. The required feed current furthermore flows withhomogeneous current density in the semiconductor junction, which iscongruent with the optical waveguide 180. See FIG. 4A. It will be notedthat the “tapered” amplifiers proposed in the above-mentioned patentsare “tapered” one dimensionally, i.e., the width varies along theoptical axis of the amplifier.

[0046] One of the novel features of one preferred embodiment of theoptical phased array according to the present invention is that thegeometry of the rib layer 150 is controlled to provide a true “tailoredindex” waveguide (amplifier) section. As seen in FIGS. 4B and 4C, therib layer 150 includes a flared or tapered portion 150 b, which extendsfrom a uniform cross-section portion 150 c to a wide end 150 d of therib layer 150, which has a much reduced thickness. It will beappreciated that the portion 150 b advantageously can be coupled to aportion 150 a, which can be one of a waveguide or an active controldevice, as discussed in greater detail below. It should be mentionedthat the active layer 130 containing one of more quantum wells isdisposed beneath both portions 150 a and 150 b of rib 150; it will beappreciated that the quantum well adjacent to portion 150 a need not bethe same quantum well adjacent to portion 150 b. It will be noted fromFIG. 4C that the lengths of portions 150 a and 150 b are L_(a) andL_(b), respectively, while the rib 150 varies between minimum andmaximum widths W_(min) and W_(max), respectively. Exemplary dimensionsare included in the discussion below.

[0047] It should be mentioned at this point that many people have triedto fabricate real index guided power amplifiers; see U.S. Pat. Nos.5,440,576 and 5,896,219. The fundamental error in all of these devicesis that the index step along the waveguide does not vary (i.e., is nottailored) and, as a consequence, these devices do not provide asufficiently stable output beam, particularly at relatively high powerlevels, i.e., greater than 0.5 watts. It is essential that the indexstep be tailored, as mentioned in the parent application, in order toensure that single mode operation can be maintained when the device isoperated at high power levels. Thus, the device disclosed in the '219patent, while it can be said to disclose a real index guided device, isnot the “tailored index” single mode device described herein. Thephysics behind the “tailored index” single mode amplifier according tothe present invention as follows. A waveguide of a given lateral widthwill only be single mode if the index step, i.e., the difference inindex from inside of the waveguide to the outside, stays below a givenvalue, i.e., maintains a predetermined ratio between waveguide width andheight. As the width of the waveguide expands (contracts), the indexstep has to decrease (increase) in order to maintain single modeoperation. If the index step is a constant, as shown in U.S. Pat. No.5,896,219, then the index step will be either too large in the widersection, thus leading to multi-mode operation, or too small in thenarrow section, leading to low efficiency, unconfined power propagation.

[0048] It should be noted that the actual shape of the flare or taperedportion 150 b advantageously can take a number of different formsincluding linear, exponential, raised-cosine, etc. In any event, it willbe appreciated that the relationship between the thickness and width ofthe flare at any point must be maintained such that the waveguide onlysupports the fundamental lateral optical waveguide mode. Though a singleend of the waveguide is shown as being wide and uniformly thin, itshould be mentioned that the invention is also realized with two flaredends and a central region of generally uniform width and thickness.

[0049] The basic flared and tapered waveguide structure with a tailoredindex according to one aspect of the present invention advantageouslycan be incorporated in any semiconductor laser irrespective of thematerials or structure of the active region. The following discussionregarding fabrication of such structures is, of necessity, merelyexemplary; it concerns the semiconductor laser structures illustrated inFIGS. 4A, 4B, 4C, and 4H (discussed below).

[0050] The preferred method for fabricating the semiconductor laserhaving such structures in FIGS. 4A, 4B, 4C, and 4H is theabove-mentioned selective area epitaxial (SAE) MOCVD growth processutilizing a flared/tapered mask geometry to obtain an appropriatecomplementary relationship between the thickness of an active regiontransverse to the axis of the waveguide geometry, or the thickness of arib-loaded waveguide geometry, and the varying lateral width of thewaveguide such that the fundamental spatial mode of operation of asemiconductor laser is maintained throughout the waveguide. As mentionedbriefly above, SAE-MOCVD results when a dielectric mask is utilized forgrowth inhibition in the masked regions. More specifically, since mostof the materials associated with MOCVD growth will not adhere to, orgrow on, a dielectric mask, these materials will diffuse on the surface,or in the gas phase, away from the masked regions and into the unmaskedregions. As a result, no growth occurs in masked regions and acorresponding, predictable increase in the thickness of selectivelygrown layers is observed in any unmasked regions in the vicinity of thedielectric mask.

[0051] In the simplest case, the dual stripe mask pattern 140 a, 140 billustrated in FIG. 4D advantageously can be utilized with substrate(layer) 140, which substrate (layer) is suitable for selective areaepitaxial growth. It will be appreciated from FIG. 4E that thedielectric mask (140 a, 140 b) produces two beneficial results. First,there is no epitaxial material grown above the masked regions; thisallows the diode laser designer to utilize the width of the openingbetween the masked regions to define the width of the laser lateralwaveguide, i.e., the core of the lateral waveguide. Second, the growthrate in the opening between the masked regions depends on both thesupply rate of growth constituents and the width of the mask stripes;the growth rate is at a maximum in the open region between the maskstripes 140 a, 140 b. The result is shown in FIG. 4E, where the rib 150exhibits an enhanced growth rate in the open area between the dielectricmask stripes 140 a, 140 b, in contrast to the growth structures 151 and152, which were grown outside of the dielectric mask and which exhibitdiminished growth the greater the distance from the center of thedielectric mask 140 a, 140 b.

[0052] Thus, selective MOCVD allows the designer to choose any layerthickness, within limits, for the central part of the structure. Thispermits the designer to select and fabricate a predetermined refractiveindex step between the core of the lateral waveguide and the surroundingregions. In fabrication of a semiconductor laser according to one aspectof the present invention, the dielectric mask advantageously includestwo flared stripe-shaped films 140 c and 140 d, having an opening widthat the narrow end of W_(min), which increases over the desired lengthL_(b) to an opening width at the wide end of W_(max), as illustrated inFIG. 4F. It will be appreciated that, in an exemplary case, the flaredrib 150 must get thinner as the flare, i.e., portion 150 b, becomeswider. In order to produce this effect, the width of the dielectricstripes 140 c, 140 d are varied, become narrower, as the flare getswider. See FIG. 4G.

[0053] It will be appreciated that this is an exemplary case regardingthe specific structure illustrated in, for example, FIG. 4C. The presentinvention is not so limited. Other variations and improvements on thedevices illustrated and processes discussed will occur to one ofordinary skill in the art after reading the instant disclosure; all suchvariations and improvements are considered to be within the scope of thepresent invention. Moreover, it will be appreciated that while thediscussion immediately above was limited to single tapered amplifierstructures providing a tailored index step, multiple tapered amplifiers,such as illustrated in FIG. 4H, advantageously can be fabricated on asingle substrate. Thus, the tailored index guided amplifier according toanother aspect of the present invention can include N such amplifiers,where N can be any positive integer.

[0054]FIG. 5A illustrates a first preferred configuration, i.e., alinear array, of an optical phased array 200 having a tailored indexsingle mode tapered amplifier structure according to the presentinvention while FIG. 5B illustrates a second preferred configuration,i.e., a two-dimensional planar array of an optical phased array 200′;FIG. 6 illustrates an alternative configuration of an optical phasedarray 200″ shown in FIG. 5A. It will be appreciated that all of theexemplary, and non-limiting, embodiments include an input port 202 foraccepting the output of a master oscillator (MO (not shown) , aplurality of turning mirrors 204 a-204 n disposed in opticaldistribution network 203 optically coupling the port 202 to a pluralityof individually controllable phase modulators 206 a-206 n (206 a′-206n′), and a plurality of real index guided power amplifier sections 208a-208 n, disposed downstream of phase modulators 206 a-206 n (206 a′-206n′), respectively. Optionally, the optical phased array illustrated inFIG. 5B can include tapered waveguides 207, each having a tailored indexthat can be used in minimizing misalignments between two integratedoptical components, e.g., the phase modulators 206 and a tailored indexsingle mode optical amplifier 208, on the array 200′.

[0055] Preferably, all of the optical elements discussed above areoptically coupled to one another in the recited order by opticalwaveguides, which can be either integrally formed or separatelyfabricated. It should be mentioned that all of the phase modulators (206a-206 n and 206 a′-206 n′) are capable of generating a 2□□phase shift,which is all that is required for the designs in both FIGS. 5 and 6.While FIG. 5 has more temporal phase delay across the optical phasedarray chip than that of the array illustrated in FIG. 6, as long as thisphase delay is less than the coherence length of the master oscillator,each emitter can be adjusted to a modulo 2□ relative phase setting toform the proper outgoing wavefront.

[0056] It will be noted that the turning mirrors 204 a-204 n illustratedin FIGS. 5A and 5B are conventional total internal reflection turningmirrors while the turning mirrors illustrated in FIG. 6 advantageouslycan be grazing incidence total internal reflection turning mirrors 204a′-204 n′. The turning mirrors in the optical phased array 200′ can bereplaced and/or supplemented by various additional optical elementsincluding, but certainly not limited to, curved waveguides anddiffractive gratings where the individual lobes generated by thediffraction grating can distribute the power to the individual waveguideeither within the epitaxial layers of the device or for free-spacelateral transmission of power (not shown individually). It should bementioned that the optical distribution network 203, including theturning mirrors 204 a-204 n, advantageously can be an activedistribution system, i.e., the optical losses normally associated with apassive distribution system can be negated by the optical gainassociated with the various optical channels.

[0057] It will be noted that the device 200′ illustrated in FIG. 5Badvantageously optical elements 210 a-210 n. Preferably, these (passive)optical elements are turning mirrors, although diffraction grating couldalso be employed. It will be noted that the use of optical elements 210a-210 n may require that the chip 200′ be mounted p-side up unless theoptical coupling is out through the substrate, which is transparent tothis wavelength. In addition, it should be noted that the distributionnetwork 203′ in FIG. 5B includes at least one stress induced indexguided optical element 203 a, which, as illustrated in FIG. 7B and asdiscussed in greater below, forces the mode into two divided lobes.

[0058] In the exemplary cases illustrated in FIGS. 5A, 5B, and 6, thetailored index single mode power amplifier sections 208 a-208 n aretapered power amplifier sections. It will be appreciated that thetailored index single mode power amplifier stages need not be “tapered,”in the sense illustrated in FIGS. 4H, 5 and 6; the essential featurerequired to make the optical phased array 200, 200′, 200″ work is thetailored index guide in the expanding amplifier region which maintainssingle mode operation along the entire length of the expandingamplifier.

[0059] It will be appreciated that one of ordinary skill in the art willimmediately perceive that there are numerous methods by which the realor tailored, e.g., tapered, index guided amplifier advantageously can befabricated. Exemplary methods that can be employed to fabricate thedevice illustrated in FIGS. 5A, 5B, and 6 include:

[0060] 1) Selective area epitaxy (SAE) which, as explained in detailabove, can be utilized in producing a continuous taper in the indexprofile of a buried rib structure. It should be mentioned that thisparticular structure is disclosed and illustrated both in the instantapplication and the parent application;

[0061] 2) Surface rib or buried rib—using a non-planar photoresistpattern, it is possible to program the erosion rate of the mask duringthe etch process to reduce the depth of the etch either piecewise orcontinuously along the expanding rib. This produces the same effect asthe buried rib structure in that the index step decreases as the modeexpands. See FIG. 4H;

[0062] 3) Current Profiling—tailor the index step by the distribution ofthe current to the device;

[0063] 4) Thermal Impedance Profiling—tailor the index step by changingthe characteristics of the thermal impedance between the junction andthe heatsink; and

[0064] 5) Impurity Profiling—the index step advantageously can becontrolled by implanting or impurity induced disordering of adjacentregions.

[0065] It will be appreciated that the tailored index guided amplifierstructure employed in the preferred embodiments of the present inventionadvantageously can utilize more than one of the above-mentionedfabrication, i.e., profiling, techniques simultaneously in order toproduce the desired, tailored index guided amplifier structure.

[0066] Taking the elements illustrated in FIGS. 5A, 5B, and 6 anddiscussing them in order would facilitate an understanding of theoptical phased array 200, 200′ having a tailored index single modeamplifier (208, 208′) structure according to one aspect of the presentinvention. Before discussing the elements themselves, it would probablybe useful to discuss the characteristics of the master oscillator.

[0067] The master oscillator (MO) that advantageously can be employedwith the present invention is preferably a real index guided devicehaving sufficient coherence length to meet the requirements of theoptical phased array according the illustrated embodiments of theinvention depicted in FIGS. 5 and 6 (discussed above) and 8 (discussedbelow). It will be appreciated that the laser beam generated by a masteroscillator having the desired coherence length advantageously can belaunched into either linear phased arrays or two-dimensional phasedarrays.

[0068] It should be mentioned that a fiber grating can be attached tothe input port 202 of the chip 200. 200′ and serve as a wavelengthselection element; this would allow the chip 200, 200′ to oscillate in asingle axial mode. It will be appreciated that this would be suitablefor single chip applications. Alternatively, a Distributed BraggReflector based master oscillator can be integrated into the device toprovide a frequency-controlled output. See U.S. Pat. No. 5,440,576 toWelch et al.

[0069]FIGS. 7A and 7B illustrate certain aspects of the techniquesemployed in fabricating one of a deep trench turning mirrors 204 a-204 napplicable to buried rib waveguides and turning mirror for surface ribwaveguides. It should be noted that surface ribs are preferred, sincethe turning mirrors can be self-aligned to rib structure. In otherwords, buried ribs require alignment marks to insure alignment towaveguide structure. For example, FIG. 7A illustrates an alignmentstructure created during buried rib growth, which is employed asreference for deep etch after p-cap growth. It should be noted that atailored index guide could be advantageous when interfacing to a turningmirror, because a lower divergence beam with greater alignment tolerancecan be realized with the tailor index structure than can be realizedwith the surface rib. In FIG. 7B, a stress index guided optical element203 a is disposed upstream of multiple turning mirrors, generallydenoted 204, when it is beneficial for the index characteristic to splitthe mode laterally into two parallel modes just before the split.

[0070] With respect to the phase modulators illustrated in FIGS. 5 and6, the phase modulators 206 a-206 n (206 a′-206 n′) advantageously canemploy any one of several well-known phase controlling techniquesincluding:

[0071] 1) Thermal Effect—A forward bias can be used to modulate thephase of the individual emitters on the device. Thermal effects are dueto the high dispersion of GaAs. As large currents are passed through thejunction, it heats up and changes the phase. While thermal effect phasecontrol has several disadvantages, i.e., the control process is slow,has multiple frequency response poles, and causes a significantamplitude modulation, it can be used in this application successfully.

[0072] 2) Electro-Optic Effect—Both linear and higher orderelectro-optic effects can be used to induce significant phase changes.However, in order to produce this effect, it is necessary to apply ahigh electric field across the junction and consequently the quantumwell. The net result is the band edge is modulated about the operatingwavelength and, consequently, the output amplitude is significantlymodulated. This method can be used, although it may be difficult todifferentiate between amplitude modulation induced by the phasemodulator and the amplitude modulation induced by the interference ofemitters. It should be mentioned that SAE techniques could be used toselectively grow a different quantum well structure, i.e., one allowingthe electro-optic effect to be used without the associated amplitudemodulation effects.

[0073] 3) Carrier Effect—The refractive index of the phase modulatorregion can also be controlled by modulating the carrier density in theregion. The carriers are generated by both the absorption of the opticalpower passing through the region and any direct current applied to theregion. Generally, the carriers are modulated by applying a reverse biasacross this region to sweep out the unnecessary carriers. Since aquantum well having a constant thickness throughout will result inundesirable absorption, it is necessary to use the SAE process to shiftthe bandgap of this region outside of the operating region and, thus,suppress the optical absorption.

[0074] 4) Displaced Quantum Well—This is the preferred technique, atleast with respect to several of the preferred embodiments according tothe present invention being discussed in detail. This technique works byshifting the PN junction toward the N side of the device. The source ofcarriers in the region will be primarily from absorption of photons fromthe adjacent regions or the signal passing through the region. Phasemodulation is achieved by applying an electric field across the quantumwell with an external bias. The photo carriers can now be depletedwithout causing optical absorption because the field is displaced awayfrom the quantum well and does not cause the band edge to shift with theapplied external bias.

[0075] It should be mentioned at this point that the phase modulatorsrequire an associated control device, e.g., a dedicated microprocessor,or system to control the output phase of each tapered amplifier stage(208 a-208 n) in the index guided tapered amplifier structure 200.Several control systems of the requisite type are disclosed in U.S. Pat.No. 5,694,408, which patent is incorporated herein by reference in itsentirety for all purposes. Additional discussion regarding the operationof the control system will be provided below.

[0076]FIG. 8 illustrates another exemplary embodiment of an opticalphased array according to the present invention, which array is anintegrated package 300 consisting of a heat sink 302 containing fluidinlet and outlet ports 304 upon which is mounted, going from left toright, a micro-controller chip 310, an interface chip 320 connected to aphase array chip 200 (200′) illustrated in FIGS. 5 and 6 via controllines 322 on a patterned substrate 324 supported by the heat sink 302,micro-optics 330 suitable for aperture filling, and an outgoingwavefront sampler 340, which will be discussed in greater detail below.It will be appreciated that the integrated package 300 is sometimesreferred to as a coherent chip. It will also be appreciated that theoptical phased array 200 advantageously can be mounted p-cap side to theheat sink 302. Preferably, the integrated package 300 includes a MEMSdevice 306, and a lock down structure 307, which permits active fiberalignment and subsequent affixing of the fiber optic. Typical devicesinclude, but are not limited to, those disclosed in U.S. Pat. Nos.6,280,100, 6,253,011, 6,164,837, 6,124,663, 5,881,198, 5,870,518,5,606,635, and 5,602,955, all of which are incorporated herein byreference.

[0077] It will be appreciated that micro-channel coolers are one form ofheat sink for dissipating the heat load generated by the integratedpackage and, thus, provide a uniform temperature distribution across thedevice. An isothermal cooler is important for this device so that all ofthe active emitters on a chip operate at the same wavelength as themaster oscillator signal

[0078] It will also be appreciated that while the micro-controller 310illustrated in FIG. 8 advantageously can be employed to provide phasealignment of an individual layer, the micro-controller 310 is notlimited to an on-board controller. An off-board micro-controller, i.e.,located off of the cooler 302, advantageously can be employed when realestate is limited. It should be mentioned at this point that the phasecontrol algorithm implemented by the micro-controller 310 does not needto be high speed for most applications, particularly since, in mostsituations, a set and forget control scheme can be utilized.

[0079]FIGS. 9 and 10 illustrate alternative structures for wavefrontsampling, either of which can be employed for, in an exemplary case, theintegrated package 300 illustrated in FIG. 8. With respect to FIG. 9, itwill be appreciated that there are two basic techniques either of whichcan be used in constructing the wavefront sampler 340, a simpledielectric mirror or a holographic grating, the latter being preferred.Thus, the wavefront sampler 340 advantageously includes a holographicdevice 342 and a detector 344. It will be appreciated that detector canbe one of several devices including, for example, a simple detector orCCD linear chip array. It will also be appreciated that while thedetector 344 is depicted as upstream of the holographic device 342, thisarrangement holds true when the holographic device is a holographicmirror. The opposite relationship would govern when the holographicdevice is a holographic lens. It should also be mentioned at this pointthat the holographic device and the micro-optics element advantageouslycan be consolidated when other design constraints permit.

[0080] In addition, a conventional waveform sampler, such as thatillustrated in FIG. 10, can be employed. As illustrated in FIG. 10, thewavefront sampler 340 is moved off chip; wavefront sampler 340′advantageously includes a beam splitter 346, e.g., a fractional beamsplitter, and an optical detector 348. It will be appreciated that whichthe arrangement shown in FIG. 10 minimizes chip real estate; the overallpackage size of the optical phased array system would necessarilyincrease.

[0081] Before discussing the operation of the phase control methodologyemployed in exemplary embodiments according to the present invention,the operation of a single tailored index single mode amplifier will bebriefly described. In FIG. 11A, a top view of the tailored index singlemode amplifier 208, which includes portions 150 a and 150 b (see FIGS.4B and 4C), while FIG. 11B contrasts the ideal index profile for asingle lateral mode laser and the index step variation provided be theexemplary embodiments of the present invention.

[0082] The operation of the phase control system discussed briefly abovewill now be described in greater detail. The control algorithm can takeone of two forms, a hill climbing loop in combination with a side lobeminimization technique and an interferometric technique. The resultsobtained without wavefront control is contrasted with the resultsobtainable using either technique in FIGS. 11A and 11B, respectively.Curve A of FIG. 11A illustrates the far-field pattern produced byn-emitters that are not coherent while Curve B illustrates the far-fieldpattern produced by n-emitters that are coherent but do not form asingle wavefront. Stated another way, Curve A illustrates the randominterference pattern generated by the phased array prior to phasealignment, while Curve B depicts the beam envelope for the incoherentsummation of the same emitters. It will be appreciated that Curve Adepicts the far-field pattern generated by the device disclosed by U.S.Pat. No. 5,440,576 to Welch et al. In contrast, FIG. 1B illustrates thesuperposition of Curve B with Curve C, which illustrates the phasealigned far-field pattern produce by the optical phased array 300depicted in FIG. 8. Inspection of Curve C reveals that it is n-timesgreater in intensity and n-times narrower in angle than the incoherentsummation of the same number of emitters (Curve B). [please check]

[0083] In the hill climbing loop technique, the on-axis intensity ismonitored as each phase setting on each emitter is tested. The settingthat increases the on-axis power is retained while all others settingsare discarded i.e. returned to their initial settings. For large arrays,the signal to noise ratio becomes very small and the final phasealignment quality is limited by the ability to see the phase test. Onemethod which increases the signal to noise ratio near convergence is touse the off-axis intensity as the feedback for the control loop. As eachphase setting on each emitter is tested, the setting that decreases theoff-axis power is retained while all other settings are returned totheir initial settings. It will be appreciated that phase tests can beperformed in integral steps ranging from a large initial test step forπ/2, then π/4, then π/8 etc. until the maximum power coupling isachieved. According to the interferometric technique, near-field phasemeasurements of each emitter are performed with either a shearinginterferometer or a modified Mach-Zender interferometer. Each phasestate is adjusted until all phase states approximately match (modulo 2π) the phase of the reference emitter or the master oscillator.

[0084]FIG. 12 illustrates a high-power laser system 400 employing aplurality of the optical phased array monolithic devices 300 depictedin, for example, FIG. 8. In the illustrated exemplary embodiment, theoutput beams of two coherent chips 300 a and 300 n are combined andlaunched into an optical network 440 by lenses 410 a, 410 a. It will beappreciated that the optical network 440 is composed of a collection ofoptical fibers 402 (most preferably EDFA (erbium doped fiber amplifier),coupled to one another by coupling devices 430 (one shown). In anexemplary case, the coupling device advantageously can be a standardcoupler such as fused bitapered couplers, although, most preferably, thecoupler is a wavelength division multiplexing (WDM) coupler (in whichlight at two different wavelengths propagating along respective fibersis coupled onto a common fiber). Preferably, the output power of thelaser system 400 can be measured using a conventional optical tap 420 ata selected wavelength and a detector 422.

[0085] It will be appreciated that optical phased arrays can be steeredonto the fiber in one or two dimensions. In either case, the maximumsteering angle is determined by the size of the emitting aperture andthe spacing between apertures. It should be mentioned that while largerdisplacements are feasible, when the displacements become too large, thecorresponding sidelobes become too great.

[0086]FIG. 13 illustrates another exemplary embodiment of an opticalphase array 500 according to the present invention, in which N of thearray packages 300 a-300 n illustrated in FIG. 8 are stacked to form atwo-dimensional array 520, each of the array packages 300 a-300 n beingsupplied with an input signal from a master oscillator 510 a-510 n,respectively. In FIG. 13, the master oscillators are off-chip; the inputsignals from the master oscillators 510 a-510 n are applied to the array520 via optical fibers 502. It will be appreciated that the masteroscillators alternatively can be integrated on the optical phased arraychip (300), i.e., the package shown in FIG. 8. It will also beappreciated that in the optical elements of the phase control subsystemadvantageously can be as illustrated in FIG. 9. Since the optical phasedarray 500 illustrated in FIG. 13 employs multiple master oscillators,the output beams produced by a single array package, e.g., 300 a, willall be, or can be made, coherent with respect to one another whileincoherent with respect to beams output by the other array packages.

[0087]FIG. 14 illustrates another exemplary embodiment of an opticalphased array 500′ where the array packages shown in FIG. 8 are againstacked to form a fully coherent phased array. Each of the opticalphased array chips assemblies are coupled through a power splittingnetwork 530 to a common master oscillator 510. The output of the twodimensional array is sampled and phase controlled according to themethods described in U.S. Pat. No. 5,694,408, which patent isincorporated herein by reference in its entirety for all purposes. Thearrangement of optical elements advantageously can be that illustratedin FIG. 10.

[0088] It will be appreciated that FIG. 10 can represent a top view ofthe optical phased array 520′ illustrated in FIG. 14. Given thatperspective, it will be understood that the fractional beam splitter 346illustrated in that figure advantageously can be employed as a beamsteering device, i.e., the output beams can be coupled out of facet ofeach of the chips 200 disposed in optical phased array 520′. It willalso be appreciated that the same effect can be obtained using eithergratings or turning mirrors. Thus a N emitter devices in the opticalphased array 520′ could be segmented into a L sets of M emitters, i.e.,M×L=N, with all beams being directed along the optical axes of the chipsgenerally denoted 200. The power amplifiers 208 a-208 n thus would feeddirectly into this beam deflector. Phase control would be as discussedabove.

[0089] As discussed above, a first embodiment of the present inventionincludes a semiconductor device constructed from at least one tailoredindex single mode optical amplifier. It will be appreciated that thetailored index step provides direct control of the real refractive indexinside of the waveguide compared to outside of the waveguide. Thewave-front or phase-front of the beam changes in response to this realindex step with the goal being to keep the wavefront substantially flatover the expanding regions. In an exemplary case, the tailored index isproduced by tailoring a current profile applied to the amplifier, theprofile varying in at least one and possibly two dimensions.Alternatively, the tailored index step can be provided by implantationof impurities in regions of the device adjacent to the amplifierstructure. Moreover, the tailored index step can be produced by varyingthe height of the buried rib in the amplifier region. When the opticalamplifier includes a heat sink, the tailored index step of the amplifiercan be provided by varying the thermal impedance characteristic of thejunction at the heatsink. It will be appreciated that the tailored indexstep advantageously can be produced by any combination of the structuralvariations mentioned immediately above, either alone or in combinationwith any other index tailoring technique known to one of ordinary skillin the art.

[0090] If desired, the semiconductor can include an optical elementcoupled to the tailored index single mode optical amplifier, whichoptical element modifies or controls the wavefront of the output signalfrom the tailored index single mode optical amplifier. Moreover, thesemiconductor can (also) include an electro-optical element, i.e., anactive element, coupled to the tailored index single mode opticalamplifier, which active optical element modifies or controls at leastone characteristic of the output signal from the tailored index singlemode optical amplifier. In an exemplary embodiment, the controlledcharacteristic is phase angle of phase delay.

[0091] It will be appreciated that the tailored index single modeamplifier advantageously can be employed as coupling means for couplingan optical signal (or signals) either into or out of the device, or intoor out of another element in the optical signal path or paths in thesemiconductor device. In an exemplary case, the signal (signals) is(are) coupled into or out of the device via an optical fiber.Alternatively, the signal (signals) is (are) coupled into or out of thedevice via a free space optical signal path. In either case, the opticalsignal path advantageously can include at least one of a signalsplitter, a modulator, a master oscillator, a waveguide of a differenttype, or other signal element known to one of ordinary skill in the art.Preferably, the input or output coupling is effected at a facet of thedevice exposing the epitaxial layers of the semiconductor device.Alternatively, the device includes a means for coupling optical signalsfrom one optical element to another with relaxed alignment tolerances inthe plane of the semiconductor while the other axis is confined andaligned by the transverse guiding layers. Alternatively, the deviceincludes means for coupling optical signals into and out of the surfaceof the device, where the input or output coupling is effected at thesurface of the device.

[0092] Stated another way, the tailored index structure advantageouslycan be employed for impedance matching a source being coupled into it oran amplified signal being coupled out of it. For example, a fibercoupling into a tapered-tailored structure would have a less restrictivealignment tolerance in at least one axis. In practical terms, thealignment tolerances in coupling from one waveguide device, i.e., aphase modulator, to another waveguide device, i.e., the tailored indexsingle mode optical amplifier, would be relaxed. If the two devices arefabricated in separate steps, this design would greatly relax thealignment tolerances that would have to be maintained. For example, a 2micron waveguide requires the accepting waveguide to be aligned towithin a tenth of 2 microns; when the waveguide is flared to 8 microns,then it only needs to be aligned to a tenth of 8 microns, or 0.8microns, i.e., a much easier problem. It will be noted that the flaredwaveguide advantageously provides both additional lateral alignmenttolerance and a better numerical aperture (NA) match to fibers or otherwaveguide devices.

[0093] It should be mentioned that the tailored index aspect of thesingle mode amplifier (or waveguide) can ease the problem of coupling asingle mode optical signal into or out of a device or chip. This isbecause the index tailoring tends to stabilize the mode over a range oftemperatures and other operating conditions, e.g., drive current intothe amplifier or waveguide, and reduce astigmatism. Thus, the opticalproblem of coupling the emission from the tailored index single modeoptical amplifier into an external optical train, e.g., path (whichcould be an optical fiber), or from an external optical train into thetailored index single mode optical amplifier, is facilitated in apractical engineering sense. The discussion which follows provides anexample of how tailored index waveguides can improve coupling into andout of certain elements in the optical signal path found in certainpreferred embodiments according to the present invention.

[0094] The discussion above referred to a “distribution network” or a“signal distribution network.” Such a network generally must incorporatesignal splitters and other optical elements for routing the opticalsignals around, for example, the chip. The latter is difficult comparedto electric signal routing on a circuit card, because photons are “lineof sight” entities; they are not easily convinced to change directions.One mechanism for routing photons through an angle (and here there is apractical maximum to the included angle, although 90 degrees is wellwithin the state of the art) in a waveguide implemented in devices suchas the disclosed embodiments of the invention is a “tuning mirror”. Thisis implemented as a vertical-walled “deep” etch, where “deep” denotes“through the photon guiding layers in the epitaxial layers of thedevice.” To implement a 90 degree turning mirror, such a mirror isetched at a 45 degree angle across a waveguide in the epitaxial layers.If a second waveguide is implemented in the epitaxial layers such thatit is a reflection of the first in the vertical wall of the turningmirror, then photons travelling down either waveguide toward the turningmirror will be reflected off the mirror, and continue outbound in theother waveguide. It will be appreciated that the mechanism describedhere is total internal reflection, which means that there is also aminimum included angle limit to these devices.

[0095] It should be mentioned that there are some important practicalproblems in implementing this type of turning mirror. Since it usuallyinvolves mask step(s) in the wafer processing different from those thatcreate the waveguides, alignment errors can arise. In extreme cases,these errors can be so severe that the reflected photons are notcaptured by the outbound waveguide, and are lost in the substrate. Intypical cases, every turning mirror imposes a signal loss—which isundesirable. One technique for reducing these losses is to taper thewaveguides as they approach the mirror. Thus the “acceptance angle” ofthe outbound waveguide is increased, and more off-angle photons aregathered—thus preserving signal.

[0096] When using a surface rib, the tapered region of the taperedwaveguides approaching the turning mirror tended to deform the mode(and, in extreme cases, split the mode). Whether this occurred on theinput waveguide or the output waveguide, it reduced the couplingefficiency through the turning mirror, and imposed signal loss. With theindex tailoring capability, the present invention provides the abilityto implement tapered (sometimes called “flared”) waveguide features atthe turning mirrors and, thus, provide increased tolerance to angle orposition errors on the turning mirrors, without incurring nearly as muchof a penalty in coupling due to mode deformation in the waveguide.

[0097] Another important consideration are waveguides that have tailoredindexes in a device (or substrate) that also has waveguides that do NOThave tailored index. To give a specific example, another common featureof on-chip distribution networks is a splitting element, i.e.,conventional T-branches and Y-branches. In these devices, it would bedesirable to physically split an optical signal according to somepredetermined ratio into two or more signals. In the case of Y-branches,this has been done by the simple expedient of forming a “Y” in thewaveguide. An optical signal arriving from the leg of the Y is split bythe point between the two branches of the Y, and the derived signalscontinue up their respective branches.

[0098] In this type of device, it is actually undesirable for the inputwaveguide to have an index characteristic that strongly selects for atight mode as it approaches the split. Rather, it is beneficial for theindex characteristic to split the mode laterally into two parallel modesjust before the split. This is exactly the tendency of a “non tailoredindex” single mode tapered waveguide—and in this case, it would becounterproductive to do anything to mitigate this tendency. Since themost useful or flexible distribution network topologies require bothwaveguide branching and turning, the distribution network according tothe present invention, which includes both tailored and non-tailoredwaveguides, accommodates both types of waveguiding functions in the samedevice or chip.

[0099] Another exemplary embodiment according to the present inventionincludes a device for generating N outputs, each having a tailored indexsingle mode optical amplifier. The device can be implemented on asingle, epitaxially grown, semiconductor substrate. If desired,additional features can be added to the device, e.g., on this substrate,to increase the functionality and utility of the device. These“features” may include, but are not limited to, phase modulators, adistribution network (with all of its possible sub-components), masteroscillator(s), and those forms of optical features that can be etched orimplanted or otherwise processed into the fabric of the substrateitself.

[0100] When the distribution network includes vertical turning mirrors(or other forms of “vertical” out-couplers) that enable the coupling ofoptical signals into and out of the surface of the substrate, then thedevice provides a two-dimensional distribution of outputs, which is notto say a rectilinear distribution). It will be appreciated that all ofthe additional features mentioned above in connection with aone-dimensional array device apply to a two-dimensional array device, solong as the device incorporates at least one vertical coupling element.

[0101] A semiconductor device comprising an optical phased array havingN output amplifiers, wherein each of the output amplifiers is a tailoredindex single mode amplifier, the N output amplifiers are disposed on asingle substrate, and N is an integer equal to or greater than 2.Preferably, each of the N tailored index single mode output amplifiershas a buried rib structure. If desired, each of the N tailored indexsingle mode output amplifiers can have a surface rib structure. If thedevice includes a heat sink, the tailored index step of the outputamplifiers is provided by varying the thermal impedance characteristicof the junction at the heatsink. Preferably, the heatsink is disposedadjacent to the N power amplifiers. In other exemplary embodiments, thetailored index step of the output amplifiers is provided by eitherimplantation of impurities in regions of the device adjacent to theamplifier structure, or tailoring a current profile applied to theamplifier, the profile varying in at least one and possibly twodimensions, or varying the height of the buried rib in the amplifierregion. It will be appreciated that the tailored index can be providedby any combination of any of the aforementioned structural variations,alone or in combination with any other technique known to one ofordinary skill in the art as being capable of varying the index of theoptical amplifier so as to produce the tailored index single modeamplifier.

[0102] It will be noted that the N tailored index single mode amplifierscan be disposed in either a linear or a two-dimensional array. Moreover,it will be noted that at least one of the input and output regions ofthe semiconductor device for the linear array correspond to a facet ofthe semiconductor device exposing the epitaxial layers of thesemiconductor device. Alternatively, the semiconductor device includescoupling elements for coupling optical signals into and out of thesurface of the device, and wherein the one or two dimensional pattern isimplemented as surface emitters or receptors from the semiconductordevice. It will be appreciated that a combination of surface and facetcouplers is possible on the same device.

[0103] It will also be noted that the semiconductor deviceadvantageously can include N optical control devices such that each ofthe optical control devices modifies or controls at least onecharacteristic of a respective optical emission from one of the Namplifiers of the device. It will be appreciated that the operation ofthe N optical control devices can one of increase the collimation of theindividual optical outputs of the amplifiers and improve the geometricfill factor in the device of the combined optical outputs of therespective amplifiers. It will be appreciated that optical controldevice connotes both optical elements (passive devices) andelectro-optical devices (active elements), e.g., a phase modulator.

[0104] In another exemplary embodiment, the semiconductor deviceincludes N (N−1) phase modulators located in the optical signal pathsupstream of the N (N−1) tailored index single mode amplifiers,respectively. Regardless of the number of phase modulators, all of thephase modulators cooperatively modify the pattern of optical emissionfrom the semiconductor device by improving the collimation of theoptical output of the semiconductor device. The semiconductor device caninclude a means of individually controlling the N (N−1) phase modulatorssuch that the phases of the output signals from each (N−1) of the Noutput amplifiers may be independently controlled with respect to eachother. In a further embodiment, the semiconductor device advantageouslyincludes an optical signal source, e.g., a master oscillator or aresonant optical cavity that gives rise to lasing. In the latterconfiguration, cavity advantageously can be (partly) formed by one ofpartially reflective coatings at any surface of the device andgrating(s) or other selectively reflecting device(s) implemented in anoptical signal path within the semiconductor device. When the only onereflective coating, device, or grating is integral to the semiconductordevice, a complementary partially reflective device can be disposedexternal to the semiconductor device to complete the resonant cavity.

[0105] Semiconductor lasers are formed when a medium has sufficient gainto overcome the round trip optical losses in the cavity. A typicalsemiconductor laser has a facet coating that is highly reflective on oneend and greater than a few percent on the other. In contrast, because ofthe high gain that can be achieved in a semiconductor laser, fabricatinga semiconductor amplifier requires very low facet reflectivities. Atypical semiconductor amplifier will have the facets antireflectioncoated with a reflectivity significantly less than 1%. Another practiceis to tilt the waveguide with respect to the output or input facets.This tilt causes a slight mode mismatch for any reflected mode at thefacet and as result helps to suppress any parasitic lasing the occurs inthe amplifier. The semiconductor devices described above all haveantireflection coatings and may incorporate a tilt at the facet toreduce the back reflections.

[0106] In a still further embodiment, the semiconductor deviceadvantageously can include a distribution network for coupling anoptical source signal to the N tailored index single mode amplifiers. Inan exemplary case, the distribution network includes waveguides andsignal splitters that route a common optical source signal to each ofthe N amplifiers so as to preserve coherence of the optical sourcesignal to each of the N output amplifiers. In an alternative case, thedistribution network includes waveguides and signal splitters that routeoptical source signals to selected ones of the N amplifiers. In eithercase, the distribution network can incorporate active waveguides thatreamplify the optical source signal (signals) to mitigate splittinglosses. Preferably, the distribution network incorporates one of at-branch, a y-branch, and signal splitting means.

[0107] A system comprising an optical phased array of N tailored indexsingle mode amplifiers, N (N−1) phase modulators disposed upstream of(selected ones of) the N tailored index single mode amplifiers, anoptical signal source producing a optical signal, and distributionnetwork for distributing the optical signal to (the selected ones of)the N (N−1) phase modulators, wherein N is an integer equal to orgreater than 2. If desired, the system can include a controller forcontrolling the N (N−1) phase modulators. Control signals generated bythe controller advantageously can be routed to selected ones of the N(N−1) phase modulators via interface circuitry. The controlleradvantageously can be responsive to a signal generated by a measuringdevice which measures parameters characteristic of selected ones of theoutput signals produced by the N tailored index single mode amplifiers.

[0108] In an exemplary case, the N tailored index single modeamplifiers, the N (N−1) phase modulators, a portion of the distributionnetwork are supported by a single support element. In that case, thedistribution network can include a free space portion. In anotherexemplary case, the N tailored index single mode amplifiers, the N (N−1)phase modulators, a portion of the distribution network, and theinterface circuitry are supported by a single support element. In afurther exemplary case, the N tailored index single mode amplifiers, theN (N−1) phase modulators, a portion of the distribution network, thecontroller, and the interface circuitry are supported by a singlesupport element. In a still further embodiment, the N tailored indexsingle mode amplifiers, the N (N−1) phase modulators, a portion of thedistribution network; the controller, the optical signal source, and theinterface circuitry are supported by a single support element. In astill further embodiment, the N tailored index single mode amplifiers;the N (N−1) phase modulators, the distribution network, the controller,the optical signal source, and the interface circuitry are supported bya single support element. In yet another embodiment, the N tailoredindex single mode amplifiers, the N (N−1) phase modulators, thedistribution network, the controller, the optical signal source, themeasuring device, and the interface circuitry are all supported by asingle support element.

[0109] With respect to the controller and measuring device, when themeasuring device measures the near-field phase pattern produced by the Ntailored index single mode amplifiers, the controller effects continuousor persistent optimization of the far-field emission of the N tailoredindex single mode amplifiers by appropriately controlling N (N−1) of thephase modulators associated with the N tailored index single modeamplifiers. In contrast, when the measuring device generates measurementsignals representing the relative phases of the output signals of the Ntailored index single mode amplifiers to each other (or to a commonphase reference signal), the controller effects continuous (persistent)optimization of the far-field emission of the N tailored index singlemode amplifiers by appropriately controlling at least (N−1) of the phasemodulators associated with the N tailored index single mode amplifiers.When the measuring means measures (estimates) the power generated by theN tailored index single mode amplifiers incident on a remote target,through a homogeneous (inhomogeneous) medium that is time-variant(time-invariant), the controller effects continuous (persistent)maximization of power from the N tailored index single mode amplifiersincident on the target by appropriately controlling at least (N−1) ofthe phase modulators associated with N tailored index single modeamplifiers. In contrast, when the measuring device measures (estimates)the power coupled from the device into an optical fiber, the controllereffects continuous (persistent) maximization of power from the Ntailored index single mode amplifiers coupled into the optical fiber byappropriately controlling at least (N−1) of the phase modulatorsassociated with the N tailored index single mode amplifiers. In anycase, it will be appreciated that the control signals generated by thecontroller permit individual control of the N (N−1) phase modulatorssuch that the phases of the output signals from each of the N tailoredindex single mode amplifiers may be independently controlled withrespect to each other.

[0110] It will be noted from the discussion above that the distributionnetwork includes waveguides and signal splitters that split andcommunicate the common optical signal source or sources to each of the Ntailored index single mode amplifiers so as to preserve coherence of thecommon optical signal source or sources to each of the N tailored indexsingle mode amplifiers. Preferably, the distribution networkincorporates active waveguides that reamplify the signal or signals tomitigate splitting losses. The distribution network can incorporatet-branches, y-branches, and other signal splitting elements known to oneof ordinary skill in the art,

[0111] As discussed above, the output signals generated by the Ntailored index single mode amplifiers can be: used independently;combined non-coherently; or combined coherently. Moreover, M of the Ntailored index single mode amplifiers can be injection locked from afundamental common optical signal, where M and N are positive integersand M is less than or equal to N. Preferably, the distribution networkroutes the common optical signal to the M of the N tailored index singlemode amplifiers; the distribution network can include a free-spaceoptical signal path.

[0112] Although presently preferred embodiments of the present inventionhave been described in detail herein, it should be clearly understoodthat many variations and/or modifications of the basic inventiveconcepts herein taught, which may appear to those skilled in thepertinent art, will still fall within the spirit and scope of thepresent invention, as defined in the appended claims. In particular, itwill be appreciated that portions or element of the exemplaryembodiments of the present invention illustrated in the various figurescan be extracted and combined to form variations of the inventionembraced by the appended claims but not expressly described; all suchvariations are considered to be within the scope of the appended claims.

What is claimed is:
 1. A semiconductor device comprising at least onetailored index single mode optical amplifier
 2. The semiconductor deviceas recited in claim 1, wherein the tailored index is produced bytailoring a current profile applied to the optical amplifier.
 3. Thesemiconductor device as recited in claim 2, wherein the current profileis tailored along the optical axis of the optical amplifier.
 4. Thesemiconductor device as recited in claim 2, wherein the current profileis tailored along at least two of the axes of the optical amplifier. 5.The semiconductor device as recited in claim 1, further comprising aheat sink, wherein the tailored index associated with the opticalamplifier is produced by varying the thermal impedance characteristic ofthe junction at the heatsink.
 6. The semiconductor device as recited inclaim 1, wherein the tailored index associated with the opticalamplifier is provided by implantation of impurities in regions of thesemiconductor device adjacent to the optical amplifier.
 7. Thesemiconductor device as recited in claim 1, wherein the tailored indexassociated with the optical amplifier is produced by varying the heightof a buried rib along the optical axis as the width varies from a firstto a second predetermined value.
 8. The semiconductor device as recitedin claim 1, wherein the tailored index associated with the opticalamplifier is produced by varying the height of a surface rib along theoptical axis as the width varies from a first to a second predeterminedvalue.
 9. The semiconductor device as recited in claim 1, wherein thetailored index associated with the optical amplifier is produced byvarying at least two of: a current profile applied to the opticalamplifier; the thermal impedance characteristic of a junction betweenthe optical amplifier and a heatsink thermally coupled thereto; impuritydensities in regions of the semiconductor device adjacent to the opticalamplifier; the height of a buried rib along the optical axis as thewidth varies from a first to a second predetermined value; and theheight of a surface rib along the optical axis as the width varies froma first to a second predetermined value.
 10. A semiconductor devicecomprising: at least one tailored index single mode optical amplifier;an input waveguide for coupling an optical signal into the opticalamplifier; and an output waveguide for coupling an amplified signal outof the optical amplifier.
 11. The semiconductor device as recited inclaim 10, wherein the output waveguide comprises an optical element forextracting the amplified signal out of a surface parallel to the opticalaxis of the optical amplifier.
 12. The semiconductor device as recitedin claim 11, wherein the optical element comprises a turning mirror. 13.The semiconductor device as recited in claim 11, wherein the opticalelement comprises a diffraction grating.
 14. The semiconductor device asrecited in claim 10, wherein the input waveguide comprises a tailoredindex waveguide.
 15. The semiconductor device as recited in claim 10,wherein the input waveguide comprises a tapered waveguide.
 16. Thesemiconductor device as recited in claim 10, wherein: the semiconductordevice comprises epitaxial layers; and at least one of the input andoutput waveguides couples one of the optical signal and the amplifiedsignal at a boundary plane of the optical amplifier intersecting theepitaxial layers.
 17. The semiconductor device as recited in claim 16,wherein the boundary plane is not perpendicular to the optical axis ofthe optical amplifier.
 18. A semiconductor device comprising: a tailoredindex single mode optical amplifier including means for tailoring astructural characteristic associated with the optical amplifier tothereby provide the tailored index; first coupling means for coupling anoptical signal into the optical amplifier; and second coupling means forcoupling an amplified signal out of the optical amplifier.
 19. Thesemiconductor device as recited in claim 18, wherein at least one of thefirst and second coupling means comprises an optical fiber.
 20. Thesemiconductor device as recited in claim 18, wherein at least one of thefirst and second coupling means comprises a free space optical pathportion.
 21. The semiconductor device as recited in claim 18, wherein atleast one of the first and second coupling means comprises a phasemodulator.
 22. A semiconductor laser device, comprising: an opticalphased array having N optical power amplifiers optically coupled to oneanother in parallel, wherein: each of the N power amplifiers is atailored index single mode guided power amplifier; and N is an integergreater than or equal to
 2. 23. The semiconductor device as recited inclaim 22, wherein each of the N tailored index single mode poweramplifiers have: a buried rib structure; and exhibit a continuous taperin the index profile.
 24. The semiconductor device as recited in claim22, wherein each of the N tailored index single mode power amplifiershave: a buried rib structure; and exhibit a discontinuous variation inthe index profile that produces a cumulative predetermined indexprofile.
 25. The semiconductor device as recited in claim 22, whereineach of the N tailored index single mode power amplifiers have: asurface rib structure; and exhibit a continuous variation in the indexprofile.
 26. The semiconductor device as recited in claim 22, whereineach of the N tailored index single mode power amplifiers have: asurface rib structure; and exhibit a discontinuous variation in theindex profile that produces a cumulative predetermined index profile.26. The semiconductor device as recited in claim 22, wherein the currentprofile applied to the amplifier structures is varied to tailor theindex of the power amplifier
 27. The semiconductor device as recited inclaim 22, further comprising a heat sink, wherein the tailored indexstep of the power amplifiers is provided by varying the thermalimpedance characteristic of the junction at the heatsink.
 28. Thesemiconductor device as recited in claim 22, wherein the tailored indexstep of the power amplifiers is provided by implanting impurities inregions of the semiconductor device adjacent to the power amplifier. 29.The semiconductor device as recited in claim 22, wherein: the N poweramplifiers are disposed in an array of M×R power amplifiers: M and R areboth positive integers; and N is equal to the product of M times R. 30.The semiconductor laser device as recited in claim 29, wherein: all ofthe N power amplifiers receive an input signal from a single masteroscillator; and the N output beams are coherent with respect to oneanother.
 31. The semiconductor laser device as recited in claim 29,wherein: a first M of the N power amplifiers receive an input beam froman R^(th) master oscillator; a second M of the N power amplifiersreceive an input beam from an R^(th−1) master oscillator; and all of theoutput beams generated by the first M of the N power amplifiers arecoherent with respect to one another but incoherent with respect to theoutput beams generated by the second M of the N power amplifiers. 32.The semiconductor device as recited in claim 22, further comprising: anoptical device for optimizing the fill factor of the phased array outputbeam synthesized from the outputs of the N power amplifiers.
 33. Thesemiconductor device as recited in claim 22, further comprising: N phasemodulators optically coupled to the N power amplifiers, respectively;and a control system controlling the N phase modulators to thereby phasealign each output signal generated by the N power amplifiers.
 34. Thesemiconductor device as recited in claim 33, wherein the control systemimplements a hill climbing algorithm.
 35. The semiconductor device asrecited in claim 33, wherein the control system implements aninterferometric phase control algorithm.
 36. The semiconductor device asrecited in claim 22, further comprising: N−1 phase modulators opticallycoupled to N−1 of the N power amplifiers, respectively; and a controlsystem controlling the N−1 phase modulators to thereby phase align eachoutput signal generated by the N−1 of the N power amplifiers.
 37. Thesemiconductor device as recited in claim 36, wherein the control systemimplements a hill climbing algorithm.
 38. The semiconductor device asrecited in claim 36, wherein the control system implements aninterferometric phase control algorithm.
 39. A high power laser systemcomprising a plurality of the semiconductor laser devices recited inclaim
 22. 40. The high power laser system as recited in claim 33,wherein the phased aligned output of the semiconductor laser device istransmitted by a single optical fiber.
 41. An integrated semiconductordevice which generates N phase aligned, wavefront matched laser beamsfrom N amplified laser beams; comprising: N phase modulators receivingthe an input beam from a master oscillator and generating N phaseshifted laser beams; and N tailored index single mode power amplifiersreceiving the N phase shifted laser beams and generating the N amplifiedlaser beams, a phase sensor generating N sensor signals indicative ofthe phase of the individual N amplified laser beams; and a controllerfor controlling the phase of each of the N amplified laser beamsresponsive to the N sensor signals, respectively, to thereby generatethe N phase aligned, wavefront matched laser beams, where N is apositive integer.
 42. An integrated semiconductor device which generatesN phase aligned, wavefront matched laser beams from N amplified laserbeams; comprising: N−1 phase modulators receiving the an input beam froma master oscillator and generating N−1 phase shifted laser beams; and Ntailored index single mode power amplifiers receiving the N−1 phaseshifted laser beams and the input beam and generating the N amplifiedlaser beams, a phase sensor generating N−1 sensor signals indicative ofthe phase of the individual N−1 amplified laser beams; and a controllerfor controlling the phase of each of the N−1 amplified laser beamsresponsive to the N−1 sensor signals, respectively, to thereby generatethe N phase aligned, wavefront matched laser beams, where N is apositive integer greater than or equal to
 2. 43. A semiconductor lasersystem, comprising: N tailored index single mode power amplifiers; Lphase modulators optically coupled to the input ports of L of the Ntailored index single mode power amplifiers; an optical device whichlaunches the output of the N tailored index single mode power amplifiersinto an optical fiber to thereby generate a coherent beam; a phasesensor for generating respective electrical signals indicative of phaseand wavefront characteristic each of L of the N coherent beams; and acontroller electrically coupled to the L phase modulators for permittingthe L phase modulators to match the phase and wavefront of the L of theN coherent beams to one another, where L and N are positive integers andN is greater than or equal to L.
 44. The semiconductor laser system asrecited in claim 43, further comprising: an optical tap for routing apredetermined portion of the N coherent beams to a sensor output port;and a power sensor optically coupled to the sensor output port formeasuring the output of the semiconductor laser system.
 45. Atwo-dimensional semiconductor laser array, comprising: an optical phasedarray having N power amplifiers optically coupled to one another inparallel, wherein: each of the N power amplifiers is a tailored indexsingle mode guided power amplifier; the N power amplifiers are disposedin an R linear arrays of power amplifiers, each linear array including Mpower amplifiers: M and R are both positive integers; and N is equal tothe product of M times R.
 46. The two-dimensional semiconductor laserarray as recited in claim 45, wherein: all of the N power amplifiersreceive an input beam from a single master oscillator; and the N outputbeams are coherent with respect to one another.
 47. The two-dimensionalsemiconductor laser array as recited in claim 45, wherein: an R^(th)linear array of power amplifiers receives an input beam from an R^(th)master oscillator; an R^(th−1) linear array of power amplifiers receivean input beam from an R^(th−1) master oscillator; and all of the outputbeams generated by the Rth linear array of power amplifiers are coherentwith respect to one another but incoherent with respect to the outputbeams generated by the R^(th−1) linear array of power amplifiers.
 48. Asemiconductor device comprising: an optical phased array having N outputamplifiers, wherein: each of the output amplifiers is a tailored indexsingle mode amplifier, the N output amplifiers are disposed on a singlesubstrate, and N is an integer equal to or greater than
 2. 49. Thesemiconductor device as recited in claim 48, wherein the N tailoredindex single mode output amplifiers are disposed in a linear array. 50.The semiconductor device as recited in claim 49, wherein at least one ofthe input and output regions of the semiconductor device associated withthe linear array correspond to a facet of the semiconductor deviceexposing the epitaxial layers of the semiconductor device.
 51. Thesemiconductor device as recited in claim 48, wherein the N tailoredindex single mode output amplifiers are disposed in a two-dimensionalplanar array.
 52. The semiconductor device as recited in claim 51,wherein the semiconductor device further comprises coupling elements forcoupling optical signals one of into and out of the surface of thesemiconductor device.
 53. The semiconductor device as recited in claim48, wherein each of the N optical amplifiers is optically coupled to oneof a surface emitter or a receptor disposed on a layer of thesemiconductor device.
 54. A semiconductor device comprising: adistribution network receiving an optical source signal and generating Ndistributed signals; N−1 phase modulators receiving N−1 of the Ndistributed signals and generating N−1 phase modulated signals; anoptical phased array having N output amplifiers, each of the N opticalamplifiers receiving one of the N−1 phase modulated signals or the Ndistributed signals, wherein: each of the output amplifiers is atailored index single mode amplifier, the N output amplifiers, the N−1phase modulators, and the distribution network are disposed on a singlesubstrate, and N is an integer equal to or greater than
 2. 55. Thesemiconductor device as recited in claim 54, wherein the N tailoredindex single mode output amplifiers are disposed in a linear array. 56.The semiconductor device as recited in claim 55, wherein at least one ofthe input and output regions of the semiconductor device associated withthe linear array correspond to a facet of the semiconductor deviceexposing the epitaxial layers of the semiconductor device.
 57. Thesemiconductor device as recited in claim 54, wherein each of the N−1phase modulators increases the collimation of the individual opticaloutputs of N−1 of the N output amplifiers.
 58. The semiconductor deviceas recited in claim 54, wherein the N−1 phase modulators collectivelyimprove the geometric fill factor of the combined optical outputs of theN output amplifiers.
 59. The semiconductor device as recited in claim54, wherein the N tailored index single mode output amplifiers aredisposed in a two-dimensional planar array.
 60. The semiconductor deviceas recited in claim 59, wherein the semiconductor device furthercomprises coupling elements for coupling optical signals one of into andout of the surface of the semiconductor device.
 61. The semiconductordevice as recited in claim 59, wherein each of the N optical amplifiersis optically coupled to one of a surface emitter or a receptor disposedon a layer of the semiconductor device.
 62. The semiconductor device asrecited in claim 59, wherein each of the N−1 phase modulators increasesthe collimation of the individual optical outputs of N−1 of the N outputamplifiers.
 63. The semiconductor device as recited in claim 54, whereinthe N−1 phase modulators collectively improve the geometric fill factorof the combined optical outputs of the N output amplifiers.
 64. Asemiconductor device comprising: a master oscillator generating anoptical source signal; a distribution network receiving the opticalsource signal and generating N distributed signals; N−1 phase modulatorsreceiving N−1 of the N distributed signals and generating N−1 phasemodulated signals; an optical phased array having N output amplifiers,each of the N optical amplifiers receiving one of the N−1 phasemodulated signals or the N distributed signals, wherein: each of theoutput amplifiers is a tailored index single mode amplifier, the Noutput amplifiers, the N−1 phase modulators, the distribution network,and the master oscillator are all disposed on a single substrate, and Nis an integer equal to or greater than
 2. 65. The semiconductor deviceas recited in claim 64, wherein the N tailored index single mode outputamplifiers are disposed in a linear array.
 66. The semiconductor deviceas recited in claim 65, wherein at least one of the input and outputregions of the semiconductor device associated with the linear arraycorrespond to a facet of the semiconductor device exposing the epitaxiallayers of the semiconductor device.
 67. The semiconductor device asrecited in claim 64, wherein each of the N−1 phase modulators increasesthe collimation of the individual optical outputs of N−1 of the N outputamplifiers.
 68. The semiconductor device as recited in claim 64, whereinthe N−1 phase modulators collectively improve the geometric fill factorof the combined optical outputs of the N output amplifiers.
 69. Thesemiconductor device as recited in claim 64, wherein the N tailoredindex single mode output amplifiers are disposed in a two-dimensionalplanar array.
 70. The semiconductor device as recited in claim 69,wherein the semiconductor device further comprises coupling elements forcoupling optical signals one of into and out of the surface of thesemiconductor device.
 71. The semiconductor device as recited in claim69, wherein each of the N optical amplifiers is optically coupled to oneof a surface emitter or a receptor disposed on a layer of thesemiconductor device.
 72. The semiconductor device as recited in claim69, wherein each of the N−1 phase modulators increases the collimationof the individual optical outputs of N−1 of the N output amplifiers. 73.The semiconductor device as recited in claim 64, wherein the N−1 phasemodulators collectively improve the geometric fill factor of thecombined optical outputs of the N output amplifiers.
 74. A laser systemcomprising: an optical phased array of N tailored index single modeamplifiers; N−1 phase modulators disposed upstream of selected ones ofthe N tailored index single mode amplifiers, an optical signal sourceproducing an optical signal, a distribution network for distributing theoptical signal to the selected ones of the N−1 phase modulators, acontroller for generating N−1 control signals; interface circuitry forapplying the N−1 control signals to the N−1 phase modulators to effectcontrol; and means for measuring a parameter characteristic of selectedones of the output signals produced by the N tailored index single modeamplifiers, wherein N is an integer equal to or greater than
 2. 75. Thelaser system as recited in claim 74, wherein the N tailored index singlemode amplifiers, the N−1 phase modulators, and a portion of thedistribution network are supported by a single support elementmaintaining the N tailored index single mode amplifiers, the N−1 phasemodulators, and a portion of the distribution network in thermalequilibrium.
 76. The laser system as recited in claim 75, wherein thedistribution network includes a free space portion.
 77. The laser systemas recited in claim 74, wherein the N tailored index single modeamplifiers, the N−1 phase modulators, a portion of the distributionnetwork, and the interface circuitry are supported by a single supportelement maintaining the N tailored index single mode amplifiers, the N−1phase modulators, a portion of the distribution network, and theinterface circuitry in thermal equilibrium.
 78. The laser system asrecited in claim 74, wherein the N tailored index single modeamplifiers, the N−1 phase modulators, a portion of the distributionnetwork, the controller, and the interface circuitry are supported by asingle support element maintaining the N tailored index single modeamplifiers, the N−1 phase modulators, a portion of the distributionnetwork, the controller, and the interface circuitry in thermalequilibrium.
 79. The laser system as recited in claim 74, wherein the Ntailored index single mode amplifiers, the N−1 phase modulators, aportion of the distribution network, the controller, the optical signalsource, and the interface circuitry are supported by a single supportelement maintaining the N tailored index single mode amplifiers, the N−1phase modulators, a portion of the distribution network, the controller,the optical signal source, and the interface circuitry in thermalequilibrium.
 80. The laser system as recited in claim 74, wherein: themeasuring means measures the near-field phase pattern produced by the Ntailored index single mode amplifiers, and the controller optimizes thefar-field emission of the N tailored index single mode amplifiers byappropriately controlling the N−1 phase modulators associated with the Ntailored index single mode amplifiers.
 81. The laser system as recitedin claim 74, wherein: the measuring means generates measurement signalsrepresenting the relative phases of the output signals of the N tailoredindex single mode amplifiers to one of each other and a common phasereference signal, and the controller optimizes the far-field emission ofthe N tailored index single mode amplifiers by appropriately controllingthe N−1 phase modulators associated with the N tailored index singlemode amplifiers.
 82. The laser system as recited in claim 74, wherein:the measuring means measures the power generated by the N tailored indexsingle mode amplifiers incident on a remote target, and the controllermaximizes the power from the N tailored index single mode amplifiersincident on the target by appropriately controlling the N−1 phasemodulators associated with N tailored index single mode amplifiers. 83.The laser system as recited in claim 74, wherein: the measuring devicemeasures the power coupled from the semiconductor device into an opticalfiber, and the controller maximizes the power from the N tailored indexsingle mode amplifiers coupled into the optical fiber by appropriatelycontrolling the N−1 phase modulators associated with the N tailoredindex single mode amplifiers.